The present invention relates to a recording apparatus for transferring a thermally fused ink image from an ink sheet to a recording sheet.
One known type of thermal-image-transfer recording apparatus utilizes an ink sheet composed of a base with a thermally fusible ink layer placed thereon and a recording sheet superimposed on the ink sheet. The ink and recording sheets are fed along against a recording head which, in response to information-dependent signals, heats and fuses ink on the ink sheet in a selected pattern to transfer a fused ink image onto the recording sheet.
The base of the ink sheet is composed of capacitor paper or various kinds of resin film, and the recording sheet comprises plain paper or various types of resin film. The recording head may be in the form of a thermal head or an electrically conductive head. Where the thermal head is employed, the ink layer of the ink sheet is heated and fused by heating elements in the thermal head which is located behind the ink sheet to apply thermal energy to the ink layer through the base or behind the recording sheet to apply thermal energy to the ink layer through the recording sheet. An electrically conductive head is used in combination with an electrically conductive platen roller. With the ink and recording sheets interposed between the head and platen roller, an electric current is passed through the ink and recording sheets to fuse a desired pattern on the ink layer due to Joule heat developed therein.
For feeding superimposed recording and ink sheets across the recording head, it has been a conventional practice to provide a single roll of such superimposed sheets and unreel them from the single roll (Japanese Laid-Open Patent Pub1ication No. 57-26239). It is therefore necessary before the sheets are placed in the recording apparatus to first produce the ink sheet, and then put it on the recording sheet and wind them together into a roll.
Setting the superimposed sheets in the recording apparatus is disadvantageous in that when the sheets are passed between the platen roller and the recording head, the sheets, particularly the ink sheet which is thin, are liable to wrinkles. Wrinkles are a source of printing errors.
During recording operation, information-indicative signals are applied to the thermal head to selectively heat the heating elements which apply heat to the ink sheet. At this time, the portion of the base of the ink sheet which is in contact with the heating elements and heated thereby is deformed by the applied heat. The deformation of the base affects the undeformed ink sheet portions by producing wrinkles therein. These wrinkles present no problem as long as they are confined close to the recorded portion of the ink sheet However, any wrinkles created further away, on the unused portion of the ink sheet, will cause defective recorded images.
Where a roll of recording and ink sheets is used, a recorded portion of the sheets is cut off by a cutter, and then the leading end of the sheets is wound back from the cutter toward a recording zone. While the recording sheets are being wound back, the unused portion of the ink sheet is likely to slacken, resulting in faulty recorded images later on. At the same time, the used portion of the ink sheet is subject to excessive tension tending to rupture the ink sheet or generate undesirable recorded image defects later on.
The recording sheet is also prone to wrinkles if it is skewed while being transferred along, and these wrinkles are also a source of recording errors.
The recording and ink sheets are susceptible to humidity; they swell wh they absorb moisture in a highly humid environment. Portions of the recording and ink sheets which are sandwiched between the platen roller and the recording head are free from the influence of humidity. When the recording apparatus is not in use for a long period of time under highly humid conditions the sandwiched sheet portion is kept from swelling, but the adjacent exposed sheet portion is deformed due to swelling. Accordingly, the sheets suffer from irregular surface deformations causing ripple-like wrinkles along the boundary between the sandwiched portion and the exposed portion. Such ripple-like wrinkles are also conducive to undesirable recording errors.
Another problem is that when the sheets remain gripped between the platen roller and the recording head for prolonged periods of time under humid conditions while the recording apparatus is not in operation, the sheets become curled along the platen roller or attach to the platen roller, and hence will not feed smoothly along during recording operation.
After an image has been recorded, the recording and ink sheets are separated from each other. When a large quantity of ink has been transferred from the ink sheet to the recording sheet, the transferred mass of ink serves as an adhesive which prevents separation of the sheets, resulting in a paper jam in the recording apparatus.
The recording sheet on which an image is recorded is cut off by a rotary cutter. At this time, any curled or bent edge of the recording sheet is apt to form a folded edge or cause a paper jam.